The technical field of the invention is optics and, in particular, devices and methods for transmitting laser radiation to optical fibers and similar light waveguides. The coupling devices and methods disclosed herein are useful in a wide variety of laser applications, including laser surgery and laser materials processing, where efficient coupling of high peak power laser radiation to a waveguide without damage is desired.
The use of lasers for surgical and industrial purposes is increasingly commonplace. In many applications, high peak power laser radiation, such as that provided by pulsed excimer lasers and the like, is employed. For example, commonly owned U.S. patent application Ser. No. 731,961 by Clarke and Muller, herein incorporated by discloses the use of excimer laser radiation to photoablate atherosclerotic lesions with minimal thermal effects or surrounding tissue damage. However, the use of high peak power lasers in conjunction with waveguides (such as optical fibers) can pose problems. Although it is typically desirable to deliver the maximum possible energy to a waveguide in a pulse of short duration, the energy is often limited by the optical damage threshold at the input face of the waveguide.
Even when the face of the waveguide is smooth as a result of polishing or cleaving of the fiber or otherwise treated to minimize reflection and scattering, optical damage will occur for input energy fluences considerably lower than the damage threshold of the bulk material of the waveguide. This imposes a limitation on the amount of energy from a high peak power laser that can be delivered through an optical waveguide. This limitation is made more severe because the intensity profile of the laser beam typically is such that the energy is concentrated at the center of beam and falls off sharply at the peripheral edges. The energy that can be coupled into an optical waveguide is thus often a function of the peak energy density incident onto the input face, rather than the average energy density. The damage threshold is further dependent on other characteristics of the laser, such as wavelength, laser energy, pulse length and beam divergence.
Since many applications of high peak power lasers require delivery through optical waveguides at high energy fluences, there exists a need for better coupling devices and methods for transmitting laser radiation without damage to waveguides. More efficient coupling devices and methods which can increase the "fill factor" of laser-to-waveguide energy coupling would satisfy a substantial need in the field of commercial optics.